Vibratory grinding method

ABSTRACT

This invention relates generally to improvements in methods and machines for grinding wheels, and particularly to methods and machines for providing intermittent pressure contact between a grinding wheel and a workpiece. In a particular embodiment of the invention, intermittent or vibratory pressure is applied to successive positions on the cutting surface of a grinding wheel in grinding contact with a workpiece by mounting a drive member or a gear having a given number of teeth on the wheel spindle for driving or meshing with a driven member or gear with an unbalanced weight distribution and having a different number of teeth from the number on the driver gear.

United States Patent Inventor Loring Coes, Jr.

Princeton, Mass. Appl. No. 795,753 Filed Oct. 7, 1968 Division of Ser. No. 597,598, Nov. 29, 1966, 1 Pat. No. 3,451,171, June 24, 1969. Patented May 25, 1971 Assignee Norton Company Worcester, Mas.

VIBRATORY GRINDING METHOD 4 Claims, 5 Drawing Figs.

US. Cl 51/281, 51/327 Int. Cl B24b l/00 FieldofSearch 51/281, 327, 33, 99

Primary Examiner-Lester M. Swingle Attorney-Allan R. Redrow ABSTRACT: This invention relates generally to improvements in methods and machines for grinding wheels, and particularly to methods and machines for providing intermittent pressure contact between a grinding wheel and a workpiece.

In a particular embodiment of the invention, intermittent or vibratory pressure is applied to successive positions on the cutting surface of a grinding wheel in grinding contact with a workpiece by mounting a drive member or a gear having a given number of teeth on the wheel spindle for driving or meshing with a driven me her or gear with an unbalanced weight distribution and having a different number of teeth from the number on the driver gear.

e r O la PATENTEDHAY25I97| SHEET 1 OF 2 wifhouf Vi brat ion surfacg 5'PeeJ. feet ,Per Mine/'66 Unbalanced ATTORNEY PATENTEUHAYZSIHYI 34579.92?

SHEET 2 OF 2 Mofor FIG. 2

l5 unbalanc 6/ gear 60 0 i if K Q a n6. 3 /-\\\\0 Nu, o

g Will! Vibration Wiihaut Vibration -/'0 5 08- Surface Sgeed, feet per: minuf C INVE TOR ATTORNEY VIBRATORY GIRDN'DWG METHOD This application is a division of application Ser. No. 597,598 filed Nov. 29, 1966, now U.S. Pat. No. 3,451,171 issued June 24, 1969, the benefit of which filing date is claimed by the applicant.

BACKGROUND OF THE INVENTION In the prior art grinding methods and machines it has been found that under constant-pressure conditions the cutting rate of a grinding wheel decreases with the time of application. The machine operators have developed hand methods for interrupting the constant-pressure contact between the grinding wheel and the workpiece in order to offset the decrease in cutting rate.

The simplest method for interrupting the pressure contact is by successively separating the spinning wheel from the work-- piece, but this requires the constant attention of the operator. In another method, the workpiece is struck by a hammer to impart a vibration to the workpiece. Vibratory motion has also been induced by striking the grinding wheel with the workpiece but in both of the last two mentioned methods there is the possibility of danger to the operators resulting from the cracking and breaking of the grinding wheels.

DESCRIPTION OF THE INVENTION It is, therefore, an object of the present invention to provide a grinding method for producing controlled intermittent pressure contact between a spinning grinding wheel and a workpiece.

Another object of the present invention is to provide an improved grinding method providing controlled vibrations in a grinding wheel.

Other objects of the invention are to provide grinding methods having improved grinding rates.

Still another object of the present invention is an improvement in the quality of surfaces cut by grinding wheels.

Further objects of the invention are reductions in grinding and laborcosts.

A particular object of the invention is to impart a frequency of vibration to a grinding wheel in the direction of work feed that differs from the wheel rotational frequency.

Still another particular object of the invention is to effect a decrease in the length of the continuous path of individual abrasive grains across the workpiece.

Further objects of the invention are the reduction in swarf erosion of the wheel and an increase in the grinding ratio.

Other objects and advantages of the present invention will become apparent upon further study of the specification, claims and the accompanying drawings wherein:

FIG. 1 shows schematically a side view of a grinding wheel after use in the grinding machine shown in FIG. 5, the wear throughout a portion of the periphery being exaggerated for the sake of clarity;

FIG. 2 is a perspective view of one kind of grinding machine that makes use of the present invention;

FIGS. 3 and 4 show graphically some of the improved results produced by this invention; and

FIG. 5 is a side view, partly broken away, showing another type of grinding machine with my invention in it.

The present invention is best explained by reference to FIGS. 1 and 5. The floor-mounted grinding machine of FIG. 5 has a stationary motor 5 operatively connected to pivot and jack shaft 8 and spindle 7 by flexible drives such as belts. The grinding wheel 10 and a gearwheel 14 which for example has 14 teeth thereon, are both secured for rotation with spindle 7. A second gear 12 having 12 teeth thereon meshes with and is driven by gear 14. Gear 12 is purposely made to be unbalanced about its axis of rotation and for this purpose an eccentrically positioned weight 13 is affixed to gear 12.

In operation the wheel is applied to the work with a force f and controlled intermittent pressure contact is maintained between the grinding wheel and the work. The intermittent pressure is produced by rotation of the eccentrically weighed gearwheel l2 and as the grinding wheel rotates the region of maximum pressure contact advances at a uniform rate around the periphery of the wheel, preferably in the direction of rotation of the wheel. Before contact between the work and wheel periphery is repeated at any one point on the periphery, the wheel makes a large number of rotations.

The successive points of contact are shown in FIG. 1 as occurring along radial lines I, 2, 3, 4, etc., with an angle a defined between the contacts. At the points of contact a higher unit pressure is applied between the wheel and the work without exceeding the available power, regardless of the size of the word. The intermittent contact caused by the relative in and out feed of the wheel decreases the continuous path of individual abrasive grains contacting the workpiece with a resulting reduction in swarf erosion and an increase in the grinding ratio.

It is preferred in the present invention to couple the grinding wheel and vibrator drives so that the ratio of the wheel vibrational frequency to the wheel rotational frequency is slightly greater than one. If this ratio is a small whole number or a simple small fraction, the operation tends to become progressively bumpy and leads to wedging, stalling and usually to breakage of the grinding wheel.

If the spindle gear has N teeth and the unbalanced gear N teeth, then at a rotational speed of w r.p.m., the vibrational frequency is w N,/ N cycles per minute. If, as preferred, N 1 N then each successive impact takes place at an angle a (N N )360/N 1 degrees in front of the previous impact point.

In the cutoff machine shown in FIG. 2, the gear 60, driven directly by the motor 15, has 60 teeth while the gear 61 on the wheel spindle in mesh with the gear 60 has 61 teeth. The motor 15 drives the unbalanced gear 60 which in turn drives the gear- 61 on the wheel spindle while at the same time producing the required vibration. The gears 12 FIG. 5 and gears 60 FIG. 2 can be unbalanced either by attaching lead weights 13 in eccentric positions, or by providing the gears with eccentrically positioned holes therethrough.

In the construction shown in FIG. 2, the motor-driven pulley 6 is not mounted directly on the grinding wheel spindle, as shown at 7 in FIG. 5. As opposed to FIG. 2, the arrangement of FIG. 5 has the advantage of not requiring the power of the motor to be transmitted through gears. Although the arrangement of FIG. 2 is satisfactory for a small or lightweight machine, it is better in a larger heavier machine such as a floor stand grinder, to keep the motor stationary, as shown in FIG. 5, so that it does not form part of the vibrating system. The grinding wheel is then driven through intermediate double pulley 8 on the pivot axis of the vibrating frame.

In the construction shown in FIG. 2 where the gears 60 and 61 have 60 and 61 teeth respectively, the impact lead angle a is 5.9, as distinguished from 5 14 in FIG. 5 where the gears 12 and 14 have 12 and 14 teeth respectively.

With the motor of FIG. 2 running at a speed of 1,500 r.p.m., the wheel motor assembly vibrates at a frequency of 1,525 cycles/minute.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the specification and claims in any way whatsoever.

EXAMPLE 1 The cutoff machine shown in FIG. 2 is powered by a fia-horsepower induction motor belted to the wheel spindle with a resulting spindle speed of 1,500 r.p.m. With the spindle gear of 61 teeth and the unbalanced gear of 60 teeth, the lead angle is 5.9". The wheel-motor assembly vibrates about its pivot point at a frequency of 1,525 cycles per minute.

Cutofi" tests were run on the machine, cutting metals and ceramics, with the unbalanced gear 60 engaged and disengaged to show the effects of vibration. The grinding wheels used were cutoff wheels selected from those disclosed in Abrasives and Grinding Wheels, copyright 1954, 1957 and 1958, by Norton Company, Worcester, Massachusetts, 1965 edition.

EXAMPLE 2 A series of cuts were made on l-inch diameter C.R. steel using the cutoff machine of example I with the unbalanced gear engaged and disengaged. The same size grinding wheel was used with two different grinding wheel specifications set forth below, under the following conditions:

A series of cuts were made on Nateo Ceramic Tile u i 3 Wheel Spindle gear 61 Unbalanced gear do 60 cutoff wheel 8 inches outside diameter X one-sixteenth inch Amount of unbalance m 366 l g cmthick X 1% inch internal diameter, having a specification 37 C v t l force lb 8 36 MOR-30 The grinding wheel was operated under the fol- Number cuts/condition 15.7 in lowing conditions: Spindle speed r.p.m 1, 500

TABLE II Wheel Cutting Wheel Time, wear, rate, specification Vibration min. in. G inJ/hr. Finish A36ROR-30 Yes 20. 49 9. 02 1. 74 46. 0 Clear. A36ROR-30. No 27.37 8.51 1.84 33.8 Slight burr and burn. A46T6B9--- Yes 16.57 0.68 23.1 57.0 D0. A46T6B9 No 22.92 0.65 24.2 41.0 Severe burr and burn.

Wheel spindle gear teeth 61 It can be seen that the use of vibration has, in each case, Unbalanced gear do- 60 reduced the cutting time by more than 25 percent at no sacriq of unbalance 366 free in grinding ratio G. The cutting costs are, therefore, ertlpal f9rce 7 reduced 25 percent. The use of vibration improved the finish Cutting tlme sec 3 spin d1 6 Speed l 500 produced in both cases.

"""""""""" It will be understood that this invention is susceptible to Eight cuts were made with the same wheel, alternating between vibration and no vibration with successive cuts.

The results obtained are shown in table I.

In the above table the Grinding Ratio G is equal to the volume of the material Cut over the volume of the wheel wear. To further illustrate the comparative data of table I and the advantages of vibration versus no vibration the curves shown in FIGS. 3 and 4 were plotted. It can be seen in FIG. 3 that the cutting rate with vibration is about 1 times the conventional normal rate. It can also be seen in FIG. 4 that this increase in cutting rate is made at no apparent sacrifice in grinding ratio. Cutting costs are, therefore, reduced about one-third.

O modification in order to adapt it to different usages and conditions and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

I claim:

1. A method of grinding a workpiece comprising:

a. rotating a grinding wheel at a given number of revolutions per minute with the working area of the wheel in contact with the workpiece;

b. intermittently increasing the pressure of said grinding wheel against said workpiece at successive nonrepetitive spaced points around said working area of the grinding wheel in contact with the workpiece; and

c. producing said intermittent pressure increases at a constant frequency different from said revolutions per minute to effect said spacing.

2. The method of claim 1, wherein the frequency of said intermittent pressure increases is greater than said revolutions per minute.

3. The method of claim 1, wherein said intermittent pressure increases cause points of higher pressure contacts to take place on said area forming the wheels periphery at points spaced from one another by a constant acute angle.

4. The method of claim 3, wherein the portion of said periphery which subtends said acute angle bears a relation to the entire periphery of said grinding wheel which is expressed as a ratio in the form of a simple fraction. 

1. A method of grinding a workpiece comprising: a. rotating a grinding wheel at a given number of revolutions per minute with the working area of the wheel in contact with the workpiece; b. intermittently increasing the pressure of said grinding wheel against said workpiece at successive nonrepetitive spaced points around said working area of the grinding wheel in contact with the workpiece; and c. producing said intermittent pressure increases at a constant frequency different from said revolutions per minute to effect said spacing.
 2. The method of claim 1, wherein the frequency of said intermittent pressure increases is greater than said revolutions per minute.
 3. The method of claim 1, wherein said intermittent pressure increases cause points of higher pressure contacts to take place on said area forming the wheel''s periphery at points spaced from one another by a constant acute angle.
 4. The method of claim 3, wherein the portion of said periphery which subtends said acute angle bears a relation to the entire periphery of said grinding wheel which is expressed as a ratio in the form of a simple fraction. 